The strike in the Sarai Darpa Khel area of the North Waziristan tribal region also wounded two suspected militants, said the officials, speaking on condition of anonymity because they were not authorized to talk to the media.

The suspected militants who were targeted were believed to be from the Afghan Haqqani network. U.S. officials consider the Haqqani network to be one of the most dangerous militant factions fighting American troops in neighboring Afghanistan. The leadership of the Haqqani network pledges allegiance to Taliban chief Mullah Omar but operates fairly independently.

U.S. drone strikes have become a serious source of tension between Washington and Islamabad. The Pakistani government regularly denounces the strikes as a violation of the country's sovereignty, even though senior officials are known to have supported some of the attacks in the past.

U.S. officials rarely provide details publicly about the covert CIA drone program in Pakistan.

Elsewhere in northwest Pakistan, militants attacked a police post before dawn Wednesday and killed six policemen, said a local government administrator, Habibullah Khan.

Ten policemen were wounded in the attack about 25 kilometers (15 miles) southeast of the city of Peshawar, said another government official, Feroz Shah. The post was staffed by both paramilitary police from the Frontier Constabulary force and also by tribal policemen.

Khan said policemen retaliated in a gunbattle that lasted several hours and killed several militants.

No one has claimed responsibility for the attack. But the Pakistani Taliban have carried out many similar attacks against security personnel in the area.